1. Field of the Invention
The present invention relates to a method of fabricating a display device, and more particularly, to a method of fabricating a liquid crystal display device.
2. Description of the Related Art
As various portable electronic devices are developed, such as mobile phones, personal digital assistants (PDA), and notebook computers, requirements for small, light weight, and power-efficient flat panel display devices have gradually increased. Presently, liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, and vacuum fluorescent display (VFD) devices have been developed for implementation as flat panel display devices. However, the LCD devices are currently being fabricated due to their simple mass production technology, easy driving systems, and production of high quality images.
FIG. 1 is a cross sectional view of a liquid crystal display device according to the present invention. In FIG. 1, an LCD device 1 comprises a lower substrate 5, which is a driving device substrate, an upper substrate 3, and a liquid crystal layer 7 formed between the lower and upper substrates 5 and 3. Although not shown, a plurality of pixels are formed on the lower substrate 5, a thin film transistor is formed at each one of the pixels, and pixel electrodes and common electrodes are formed on the lower and upper substrates 5 and 3, respectively. The upper substrate 3 is a color filter substrate that includes a color filter layer for producing colored light. In addition, an alignment layer is formed on the upper substrate 3 for orienting liquid crystal molecules of the liquid crystal layer 7.
The lower substrate 5 and the upper substrate 3 are attached by a sealing material 9, and the liquid crystal layer 7 is formed therebetween for driving the liquid crystal molecules using the driving devices formed on the lower substrate 5 in order to control light transmitted through the liquid crystal layer. Processes for fabricating the LCD device can be divided into a driving device array substrate process, wherein the driving devices are formed on the lower substrate 5; a color filter substrate process, wherein the color filters are formed on the upper substrate 3; and a cell process.
FIG. 2 is a flow chart of a method for fabricating a liquid crystal display device according to the related art. In FIG. 2, a step S101 includes forming a plurality of gate lines and a plurality of data lines on a lower substrate using a driving device array process for defining a plurality of pixel areas, and includes formation of thin film transistors, which are connected to the gate lines and the data lines, at the pixel areas. In addition, a pixel electrode, which is connected to the thin film transistor through the driving device array process, is formed for driving a liquid crystal layer as a signal is transmitted through the thin film transistor.
A step S104 includes formation of a color filter layer of R, G, and B colors and a common electrode on an upper substrate using a color filter process.
Steps S102 and S105 both include formation of alignment layers on the upper and lower substrates, wherein the alignment layers are rubbed in order to provide the liquid crystal molecules of the liquid crystal layer formed between the upper and lower substrates with an initial alignment and surface fixing force (i.e., pre-tilt angle and orientation direction).
Step S103 includes scattering a plurality of spacers onto the lower substrate for maintaining a uniform cell gap between the upper and lower substrates.
Step S106 includes formation of a sealing material along an outer portion of the upper substrate.
Step S107 includes attaching the upper and lower substrates by compressing the upper and lower substrates together.
Step S108 includes dividing the attached upper and lower substrates into a plurality of individual liquid crystal panels.
Step S109 includes injection of the liquid crystal material into the liquid crystal panels through a liquid crystal injection hole, wherein the liquid crystal injection hole is sealed to form the liquid crystal layer.
Step S110 includes testing the injected liquid crystal panel.
Operation of the LCD device makes use of an electro-optical effect of the liquid crystal material, wherein anisotropy of the liquid crystal material aligns liquid crystal molecules along a specific direction. Accordingly, control of the liquid crystal molecules significantly affects image stabilization of the LCD device. Thus, formation of the alignment layer and the spacers are critical for fabricating an LCD device that produces quality images.
However, during the spacer scattering process, the spacers are provided with the pixel area through which the light is to be transmitted. Accordingly, the spacers within the pixel area are similar to an impurity that interrupts orientation of liquid crystal molecules, thereby lowering aperture rate. Thus, a distribution density of the spacers should be controlled and uniformly maintained across a display screen of the LCD device. For example, although the distribution density of the spacers is high and a uniform cell gap may be maintained, displaying functions of a black screen is lowered by light dispersal due to the spacers, and a contrast ratio is reduced.
In order to solve the above problem, patterned column spacers are formed at desired locations by photolithographic processes of depositing (coating), developing, and etching organic polymer material. In addition, a mask process must be added in order to form the column spacers, thereby increasing fabrication costs and complicating the overall fabricating processes. However, formation of the spacers using the scattering method is performed after formation of the alignment layers, whereas using the patterned column spacers means that the formation of the alignment layers is performed after formation of the patterned column spacers. For example, the alignment layer process commonly uses a roller coating method.
FIG. 3 is a schematic view of a method for forming an alignment layer using a roller coating method according to the related art. In FIG. 3, an alignment material 21 is uniformly supplied between an anylox roll 22 and a doctor roll 23 of cylindrical shape as the anylox roll 22 and the doctor roll 23 rotate. The alignment material 21 is provided using a dispenser 1 having an injector shape. Then the alignment material 21 formed on a surface of the anylox roll 22 is transferred onto a rubber plate 25 when the anylox roll 22 rotates to contact a printing roll 24 upon which the rubber plate 25 is attached. The rubber plate 25 is aligned with a substrate 26 upon which the alignment material 21 will be applied. As a printing table 27, upon which the substrate 26 is loaded, is moved to contact the printing roll 24, the alignment material 21 is transferred onto the rubber plate 25 and is re-transferred onto the substrate 26 to form an alignment layer (not shown). Since a thickness of the alignment layer is about 500-1000 Å, thickness differences of 100 Å of the alignment layer may generate a blot on the screen of the LCD device. Accordingly, uniform thickness of the alignment layer is critical to display quality images on the screen of the LCD device.
However, since the dispenser 1 supplies the alignment material 21 onto the anylox roll 22 using a left-to-right motion along an upper part of the anylox roll 22, uniform thickness of the resulting alignment layer may not be achieved. For example, as a size of the substrate 26 increases, it becomes increasingly more difficult to form the alignment layer having a uniform thickness. Moreover, since all of the alignment material 21 transferred on the rubber plate 25 is not necessarily re-transferred onto the substrate 26, a significant amount of the alignment material 21 is wasted as compared to the amount of alignment material 21 that is re-transferred onto the substrate 26. Accordingly, the amount of wasted alignment material 21 unnecessarily increases production costs.